This invention concerns improvements in the processing of video image signals to achieve so-called digital video effects.
In such processing, each field frame of a television image is stored as a series of discrete digital values or pixels containing the luminance or chrominance information of the original signal and obtained by sampling the original signal at an appropriate pixel repetition rate. The original signal may be reproduced by scanning the store, or, by addressing the store in appropriately timed relation to synchronising signals defining the television raster, selected image information can be retrieved from the store and displayed on a television screen in any desired position or orientation. Such retrieved information may be combined with other image information to produce a pattern or collage of discrete images, and by moving the boundaries between respective patterns containing the separate picture information, various effects can be achieved, such as the so-called "wipe" effect where one image is progressively replaced for another.
The geometrical pattern within which processed picture information is to appear on the image screen may be computed, for example by a microprocessor, in response to appropriate input controls, and, from output signals from the microprocessor identifying the pattern, it is necessary to derive appropriate control signals to enable the corresponding addressing of the image store and/or the control of image display.